One-way, flap-type pressure relief valves are commonly used in applications such as vehicle ventilation systems. Typically, the valve serve to relieve over-pressure that can occur within a nearly air-tight passenger compartment of a vehicle when, for example, a door of the vehicle is rapidly closed, while preventing the entry of air from outside the vehicle into the passenger compartment.
Valves used for this purpose generally include a frame or housing for mounting within an aperture formed in a panel enclosing the passenger compartment and defining an air passageway through the panel. The housing has one or more internal valve seats over which a plurality of valve flaps lie. The flaps include relatively thin, flexible members and overlie the valve seats on a side of the housing facing exterior of the passenger compartment. Each flap is fixed to the housing along one peripheral edge.
When an over-pressure condition occurs within the passenger compartment, the air pressure forces the flaps to move away from the valve seats, bending or hinging adjacent the fixed edge to allow air to flow through the air passageway out of the passenger compartment. When the air pressure has equalized on both sides of the valve or when the pressure on the exterior becomes greater, the flaps swing or bend back to engage the valve seats and block airflow into the passenger compartment.
Valves of this general type are often manufactured by injection molding the housing and the valve flaps as separate pieces and then joining the two components by any one of several different methods. U.S. Pat. No. 5,601,117 teaches that apertures formed along an edge of the flap are placed over pins projecting from the corresponding portion of the housing. The ends of the pins are then flattened to form locking caps which secure the flap over the pin. U.S. Pat. No. 5,419,739 discloses a valve flap in the form of a flexible sheet having integrally formed tabs which are forced through respective slots formed in the housing. Each of these various methods of construction has inherent disadvantages, generally related to the fact that producing separate components that must be assembled with one another is time consuming and/or labor intensive, thus making the valve relatively expensive to manufacture.
U.S. Pat. No. 5,355,910 discloses a valve having a flap element formed by extruding a sheet of relatively soft, flexible elastomeric material, and simultaneously extruding one or more strips of relatively rigid plastic onto the surface of the sheet. A first of the strips provides a rigid mounting strip for bolting or otherwise joining the valve element to an associated valve housing. A second of the rigid strips can be formed to extend across the width of the flap adjacent the opposite edge thereof to prevent the valve element from warping or deforming during use. The gap between the mounting strip and the stiffening strip forms a flexible hinge where the flap bends to move between closed and open positions. The continuous extrusion is sheared to the length required for use in a valve assembly, and apertures are formed through the mounting strip so that the flap can be secured to the valve housing.
The extrusion technique requires the rigid strip to extend the full width of the flexible sheet and be a constant thickness and height. The extrusion technique is also unable to produce a plurality of flaps joined together in a top-to-bottom arrangement so that the flaps can then be attached to the valve housing in a single assembly step.